15 January 2012

I always prefer to visit a bridge before covering it here, but I have no plans to go anywhere near Norwich soon, and this bridge looked worth featuring.

It opened to the public last month, and spans the River Wensum in Norwich city centre. Spanning about 30m, it is 80m long in total, shaped like the letter "J" in plan. Designed by Ramboll, it is named for Peter Jarrold, who first came up with the idea for a bridge at this site twenty years ago.

The bridge's form is unusual - there are plenty of bridges with curved decks like this, but very few with so little obvious means of support. Most are suspended from arches, or masts, or less frequently held up by larger girders or trusses.

Peter's Bridge is built primarily in weathering steel, with a torsionally stiff box girder on the inner edge of the curve, supporting braced steel ribs. The deck has a wedge-shaped cross-section, emphasising the outer edge and making it look thinner than it really is. The deck cross-section of York Millennium Bridge has several similarities. The photos are unclear, but there appear to be a small number of very slender supports below the main edge girder.

The parapets are a combination of weathering steel uprights with stainless steel handrails and, on the outer face, mesh infill. It's a combination of materials that can be very attractive, as I've illustrated here before. However, it's also prone to vandalism and to the risk of rapid corrosion due to trapped water, particularly in the British climate.

Here, timber panels are used to prevent direct contact with the rusty inner face of the support girder, although I would not be surprised to see graffiti on the outer face of the girder in the future - this is difficult to clean off without creating a patchy finish. The deck is also timber-planking, with gaps allowing rainwater to drain straight through, and it will be interesting to see how well that performs or whether trapped moisture affects the support ribs over time.

Quibbles aside, the overall appearance is daring without unnecessary flamboyance, and it looks like a fine new structure, nicely detailed.

12 January 2012

Will 2012 Deliver Promised New Frontiers? The Margaret Hunt Hill Bridge
What will Calatrava's new bridge mean for Dallas? "Will its legacy mark a shift in civic thinking, leading to new models of development and forward-thinking urban practice? Or will it serve as yet another symbol of Dallas’ bloated ego, its propensity to invest in the loud and the most expensive as part of the perpetual pageantry of gregarious societal theatrics?"

For even greater bile and hyperbole, on the occasion of the switch-on of the bridge's lighting, see this Dallas Observer blog.

World's tallest bridge hailed in Mexico
The virus that the Baluarte Bridge is the "world's tallest bridge" seems to have spread widely across the web, and the good old BBC were one of many news organisations who played their part in spreading it. Even New Civil Engineer, who should know better, perpetuated the meme before correcting their story a few days later.

Why was this bridge allowed to decay?
If the author is to believed, a rare example of a surviving James Dredge suspension bridge (Victoria Bridge, in Bath) has deteriorated severely, largely due to an incorrect assumption that developer funding would save the local council from having to look after it properly. The slightly more measured account from the council suggests work is in hand to prop and eventually refurbish the bridge, to reopen it in 2013.

Out of a town population of 55,750 or so, a massive 60 people voted for this design in a public consultation, against 77 people preferring an alternative. The new 35m span bridge will have twin tubular arches.

A planning application is expected later this year, with construction expected to start in mid-2013.

05 January 2012

I strongly suspect 2012 is going to be a fairly quiet year here at The Happy Pontist. The myriad obstructions which clutter "real life" have obliged a fever of activity, both necessary and unnecessary, which will leave limited time for my more idle whims such as blogging.

With this in mind, it's perhaps appropriate that my first post of the year is to feature a book, Colin Sackett's "River Axe Crossings: from Mouth to Source" (2008, www.colinsackett.co.uk), in which bridges are essentially conspicuous by their absence.

Opening the book from what is normally seen as the "front", it is titled "Upstream: River Axe Crossings from Mouth to Source". Each right-hand page then offers a picture of the River Axe looking upstream, photographed from each of forty-one consecutive river crossings (weirs, fords and rail bridges are excepted, not unreasonably). This takes the reader on a journey through Devon, Somerset and Dorset, all predominantly rural counties in England's south west.

Opening from the "back", the book's title is "Downstream: River Axe Crossings from Source to Mouth", and every left-hand page depicts ... oh, you probably guessed already. The photographs taken at the river crossings are bookended by images from the river's source and mouth.

Every photograph is in black-and-white, and accompanied by a brief paragraph with details on the crossing in question, or on what can be seen in the distance. The change in appearance of the river and its banks from a tightly constrained woodland watercourse, through open fields, back through woodlands, and eventually into a wide, open floodplain is quietly interesting, and a remarkably informative way to consider the details of a highly particular landscape. You can find some example images from the book at the author's website.

Although the book is clearly a one-off, it's easy to imagine a series of similar volumes depicting other rivers, or imposing order on entirely different features of the landscape. I'm reminded of the artist Richard Long, and his landscape journeys planned according to imposition of an artificial geometry onto a survey map (one example). There is a similar sense of using an entirely arbitrary system to order a journey and hence disrupt the way we normally encounter the landscape.

Many of the photographs make clear how this particular river, flowing as it does through a floodplain of varying width, both determines how people have altered the landscape, and is affected by human actions. The nature of the river banks, often in deep cut, reflects the use of the river as a boundary, as well as its diversion past other boundaries. It also makes clear the predominantly agricultural nature of the area, cleared of vegetation which might restrict the river's ability to erode and meander.

Bridges do appear occasionally, in the distance, where they can be seen from another crossing, or by implication, whenever an image has clearly been taken from the perspective of a taller span. Although they define the entire structure of the book, they are invisible platforms, present only because they allow the photographer to stand on the centreline of the channel without getting his tripod wet. Nonetheless, you can tell a little about their nature by considering the gaps between the photographs - stretches of the river which don't merit a crossing, or where one is uneconomic.

As a pontist who normally photographs bridges as an object in their own right (the structural engineer's focus) or as an object within a landscape (a nod to architectural friends), the absence of bridges from this book of river crossings comes as something of a shock, but a welcome one. It's too easy for an engineer to forget that bridges are not only there to cross, but to stand upon, that they establish a relationship not just between the two river banks but also allow their user a very different perspective upon their surroundings.

Post-structuralists in literature have long been au fait with the possibility for the author to disappear from the text. Perhaps it is time for post-structural pontists to likewise celebrate the disappearance of bridges from the landscape.